Electrically driven oxygen separators incorporate an electrolyte that is formed of a ceramic that is capable of conducting oxygen ions at elevated temperatures. An electrical potential is applied to opposite sides of the electrolyte through cathode and anode electrodes. The oxygen ionizes at the cathode and oxygen ions are driven through the electrolyte. The oxygen ions recombine with the anode with the loss of electrons.
For example, in U.S. Pat. No. 5,871,624, a series of modules is formed by injection of molding in ionic conducting ceramic electrolyte. The molded device has a series of tubes that extend from a general planar tube support member. The outer surfaces of the tubes and the interior of the tubes are coated with electrically conductive materials to form electrode surfaces separated by the electrolyte. Electrical connections to the electrodes are made through vias or holes extending through the ceramic electrolyte.
The aforementioned modules may be connected together and housed within a furnace in which the electrically driven oxygen separators are heated to their operational temperature by means of electrical heaters. An oxygen containing gas, for example air can be introduced into the furnace by way of a blower. A conduit in the form of a product tube is connected to oxygen separators to discharge the separated oxygen from the electrically driven oxygen separators. The product tube can be attached to the electrolyte by a glass seal such as described in U.S. Pat. No. 6,532,769. In order to provide thermal expansion capability between the product tube and the electrolyte, the product tube is fabricated from the same material as the electrolyte. For example, if the electrolyte were fabricated from gadolinium dopes ceria, the product tube can be fabricated from gadolinium doped ceria. Since the power supply is grounded and such a product tube, can, at least to a limited extent, be electrically conductive, a shock hazard is presented that is overcome by grounding the product tube.
It has been found, however, that where the product tube is formed of the same material as the electrolyte or other ionic conductive material, over time, the tube will decompose due to electrochemical reduction reactions between the ceramic due to an electrical potential that exists along the length of the product tube, between the electrically driven oxygen separators and ground due to the grounded power source.
It is to be noted that in other type of electrically driven oxygen separators, an inlet conduit is provided to introduce an oxygen containing gas into the electrically driven separator or separators and an outlet conduit is provided to discharge oxygen depleted retentate from the separator. Since such electrically driven oxygen separators are also powered by a grounded power source and the inlet and outlet conducts are grounded, the inlet and outlet conduits can again be subject to an electrical potential and also degrade over time.
As will be discussed, the present invention provides an electrochemical cell assembly that utilizes a material in the fabrication of the conduit, used either as the product tube or other conduit connected to the electrically driven separator that is designed to prevent such deterioration as discussed above by virtue of its electrically insulating and electrochemical reduction resistive properties.